1. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess PlateauInstitute of Soil and Water ConservationNorthwest A&F University Yangling 712100 People's Republic of China
2. Institute of Soil and Water Conservation of Chinese Academy of Sciences and Ministry of Water Resources Yangling 712100 People's Republic of China
3. Shanxi Agriculture University Taigu 030800 People's Republic of China